Genome engineering technology has the capability of resolving many unmet needs in the field of gene therapy. Among the newly developed genome engineering tools, the Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR) System has revolutionized genome editing due to ease of engineering and programmability. Despite its tremendous potential, CRISPR for gene therapies faces several challenges. To be successful, CRISPR must be specific and have minimal off-target effects both in genome and cells/tissues. As such, precise detection of off-target effects on the genomic loci is another important factor that has received considerable attention so far. Efficient translation of CRISPR to human trials requires human-based platforms that can provide direct information about the biological consequences of genome editing. Most studies so far have been conducted in cell lines or animal models. Little progress has been made to examine the gene editors in platforms that can yield human relevant readouts and enable us to rapidly assess and predict adverse effects of CRISPR in physiologically relevant human models. Human organ on-a-chip platforms can facilitate studies on the safety of genome editing technologies and delivery systems in human. We hypothesize that human liver on a chip can be adopted for accurate assessment of toxicity and off-target activity of CRISPR-based gene editing ex vivo. In aim 1 we will investigate cellular innate response to Cas9 protein or gRNA in a complex human liver on a chip platform: We hypothesize that human liver on a chip platform can be employed to accurately predict cellular stress response to Cas9 protein, gRNA or delivery vehicles in primary human liver cells. In aim 2 we will examine CRISPR off-target activity in primary human liver cells within liver on a chip: We hypothesize that our human liver on a chip platform can be used to examine CRISPR off target cleavage in primary liver cells ex-vivo. Using a library of clinically relevant liver genes and designed gRNAs with different specificities, we will investigate CRISPR off-target activity and verify a set of transcriptomic or secretory factors in liver tissue that can serve as future markers for evaluation of CRISPR off target activity. In aim 3, we will understand the role of micro-environmental cues in CRISPR adverse effect on human liver cells in a chip. We will test the impact of mechanically non-rigid hydrogel-based scaffolds and low-grade inflammatory conditions in CRISPR gene editing efficiency in human tissue formed ex vivo.